Clone REA1227 recognizes the mouse CD267 antigen, a type III transmembrane protein receptor that binds to APRIL and BAFF and also interacts with heparan sulfate proteoglycans (HSPGs). Expression of CD267 is found on subset of T cells, marzinal zone (MZ), and B1 B cells. A dual role of TACI has been suggested in regulating B cell activation. TACI–/–
mice have high number of hyper-reactive B cells, indicating an inhibitory role of TACI. On the other hand, mice lacking TACI are unable to mount normal T cell independent type 2 (TI-2) immune response and thus suggesting a positive role in promoting B cell activation.